1. Field of the Invention
The present invention relates to a motor controller for driving a motor using an electric converter which incorporates power elements.
2. Description of the Prior Art
A prior art motor controller which controls a current to be applied to a motor by controlling the switching of power elements will be described hereinunder.
FIG. 17 is a block diagram showing the constitution of a prior art motor controller. This is an example of car motor controller to be mounted on a vehicle and a three-phase AC motor is used as a motor.
In FIG. 17, reference numeral 1 denotes a motor controller, 2 a motor, 3 an arithmetic and control unit, and 4 a power conversion semiconductor as a power converter. The power conversion semiconductor 4 has three phase switching arms (U-phase arm, V-phase arm, W-phase arm). The U-phase arm, one of the switching arms, comprises an upper arm switching element 5a, lower arm switching element 5b, upper arm free wheeling diode 6a and lower arm free wheeling diode 6b. The V-phase arm and the W-phase arm have a similar structure and comprise upper arm switching elements 5c, 5e, lower arm switching elements 5d, 5f, upper arm free wheeling diodes 6c, 6e and lower arm free wheeling diodes 6d, 6f, respectively. One switching element 5 (5a to 5f) and one free wheeling diode 6 (6a to 6f) constitute one power element 7 (7a to 7f). Denoted by 8 (8a to 8c) are U-phase, V-phase and W-phase current detectors arranged on power lines for the motor 2 external to the power conversion semiconductor 4.
As shown in the figure, two power elements 7 are connected in series for each phase of three-phase AC. One power element connected to the high potential side of DC power input is called xe2x80x9cupper armxe2x80x9d and the other power element connected to the low potential side of DC power input is called xe2x80x9clower armxe2x80x9d.
A description is subsequently given of the operation of this motor controller.
The motor controller 1 converts DC power from an unshown power source into AC power and supplies the AC power to the motor 2. The conversion of DC power into AC power is carried out by switching the switching elements 5 constituting the power elements 7 of the power conversion semiconductor 4. The arithmetic and control unit 3 computes a current instruction value to be applied to the motor 2 to cause the motor 2 to carry out desired operation and generates gate drive signals for turning on or off the switching elements 5 so that a current corresponding to the current instruction value runs through the motor 2. The gate drive signals are transmitted to the gates G of the switching elements 5 of the three phases.
The control of the motor 2 by a vector control method which is frequently used to control the generation torque of the motor 2 accurately will be described hereinunder.
In this method, the amounts of voltage and current of three-phase AC are decomposed into vectors which are plotted on the axis (d axis) of coordinates rotating in the same direction as a magnetic flux and the axis (q axis) of coordinates rotating in a direction perpendicular to the above direction to control generation torque by controlling voltage and current on the rectangular coordinates.
The relationship between voltage and current on the rotary rectangular coordinates (d and q coordinates) is represented by the following expression when a permanent magnet type synchronous machine is used as the motor 2:                               [                                                                      V                  d                                                                                                      V                  q                                                              ]                =                                            [                                                                                          R                      a                                                                                                                          -                        ω                                            ·                      L                                                                                                                                  ω                      ·                      L                                                                                                  R                      a                                                                                  ]                        ·                          [                                                                                          i                      d                                                                                                                                  i                      q                                                                                  ]                                +                      [                                                            0                                                                                                  ω                    ·                                          φ                      a                                                                                            ]                                              (        1        )            
wherein Vd is the voltage of the d axis, Vq is the voltage of the q axis, id is the current of the d axis, iq is the current of the q axis, Ra is a primary resistance, L is an inductance, xc3x8 a is the magnetic flux of the magnet and xcfx89 is a rotation angle speed.
The generation torque xcfx84m of the motor 2 at this point is represented by the following expression:
xcfx84m=Pmxc2x7xc3x8axc2x7iqxe2x80x83xe2x80x83(2)
wherein Pm is the polar logarithm of the motor 2.
The polar logarithm Pm and the magnetic flux xc3x8 a are fixed by the motor 2, and the adjustment of the generation torquexcfx84m is carried out by controlling the amount of the current iq of the q axis. Therefore, the accurate control of the motor 2 means the accurate control of the generation torque of the motor 2, that is, the amount of the current iq of the q axis. Therefore, three-phase AC running through the motor 2 is detected by the current detectors 8 and decomposed into vectors on the d axis and q axis to compute the current id of the d axis and the current iq of the q axis. Further, voltage Vd on the d axis and voltage Vq on the q axis are computed from id and iq to obtain desired generation torque xcfx84m based on which gate drive signals are generated.
Since the control accuracy of generation torque is connected with the acceleration and deceleration of a vehicle when the car motor controller 1 is used for an electric car using the motor 2 as a drive source, it is an important factor which affects riding comfort. When the car motor controller 1 is used for a hybrid car which uses the motor 2 and an internal combustion engine as drive sources, control accuracy becomes more important because both the generation torque of the motor 2 and the generation torque of the internal combustion engine are controlled in a well balanced manner to reduce fuel consumption and harmful substances contained in exhaust gas. Thus, high control accuracy is required of the car motor controller 1. As described above, since a current running through the motor 2 is detected by the current detectors 8 to control the generation torque of the motor 2 directly, high-accuracy control is possible.
However, since the current detectors 8 are arranged external to the power conversion semiconductor 4 to detect the three-phase current of the motor 2 in the prior art motor controller 1, fixing members constituting the current detectors 8 are required and also signal lines for connecting the current detectors 8 to the arithmetic and control unit 3 are required, thereby increasing the number of assembly steps. Further, when these signal lines are affected by noise and exert a bad influence upon detection current values, or disconnected due to the deterioration of a harness after long-time use or the loose contacts of connectors, they cause a sudden change in generation torque during operation. This may impair the continuity of control of the car motor controller 1 and exert a bad influence upon the behavior of a vehicle.
To overcome the above problems, a motor controller described below has recently been developed.
In the motor controller disclosed by Japanese Laid-open Patent Application No. 11-149928 which was filed by the present applicant, current detectors which have resistance characteristics are used, arranged on the same substrate as power elements and built in a power conversion semiconductor, and the power conversion semiconductor and an arithmetic and control unit are stored in the same container.
This eliminates an increase in the number of assembly steps caused by the external arrangement of the current detectors, reduces the number of constituent elements and the number of trouble possible sites, and shortens the signal lines between the current detectors and the arithmetic and control unit, thereby reducing the influence of noise.
In the motor controller which comprises current detectors having resistance characteristics, arranged on the same substrate as power elements and stored in a power conversion semiconductor, the current detectors have such a problem that the reliability of current values detected by the current detectors is low because the current detectors are readily affected by changes in ambient environment, particularly temperature variations. This tendency is marked when the current detectors are arranged external to a vehicle because changes in ambient environmental temperature are large. This leads to the deterioration of control accuracy and a reduction in the durability of the current detectors themselves.
It is an object of the present invention which has been made to solve the above problems to provide a motor controller which improves the reliability of motor control and enables stable and high-accuracy control by detecting current values running through the motor by means of current detectors by preventing changes in ambient environment, particularly the influence of temperature variations.
According to a first aspect of the present invention, there is provided a motor controller for controlling an application current to a motor, which comprises a power converter incorporating power elements, current detectors arranged on power lines for connecting the power elements to the motor, and an arithmetic and control unit for controlling the switching of the power elements using detection currents from the current detectors, wherein the arithmetic and control unit comprises a storage unit for storing current detection characteristic compensation data for compensating for fluctuations in the characteristics of the current detectors, current value computing means for computing current values by correcting detection currents from the current detectors based on the current detection characteristic compensation data, and means for computing and generating drive signals for controlling the switching of the power elements based on the computed current values.
According to a second aspect of the present invention, there is provided a motor controller for controlling an application current to a motor, which comprises current detectors arranged on power lines for connecting power elements in a power converter to the motor and an arithmetic and control unit for controlling the switching of the power elements using detection currents from the current detectors, wherein the controller further comprises an ambient temperature detector for detecting the ambient temperature of the arithmetic and control unit and current value computing means for computing current values by correcting detection currents from the current detectors so that the arithmetic and control unit compensates for changes in the constants of electronic circuit parts in the arithmetic and control unit caused by temperature variations based on the detected ambient temperature.
According to a third aspect of the present invention, there is provided a motor controller, wherein an ambient temperature detector for detecting the ambient temperature of the arithmetic and control unit is provided, and current value computing means for computing current values by correcting detection currents from the current detectors based on current detection characteristic compensation data carries out a compensation operation for compensating for changes in the constants of the electronic circuit parts in the arithmetic and control unit caused by temperature variations based on the detected ambient temperature to compute the current values.
According to a fourth aspect of the present invention, there is provided a motor controller, wherein the current detectors are built in the power converter, and the power converter and the arithmetic and control unit are stored in the same container.
According to a fifth aspect of the present invention, there is provided a motor controller, wherein the power converter and the arithmetic and control unit are stored in the same container, current detectors having resistance characteristics are used and stored in the power converter, temperature detectors are provided near the current detectors, a storage unit prestores cur rent detection characteristic compensation data for compensating for fluctuations in the characteristics of the current detectors caused by the temperature variations, and current value computing means computes current values by correcting detection currents from the current detectors based on detection temperatures from the temperature detectors and the current detection characteristic compensation data.
According to a sixth aspect of the present invention, there is provided a motor controller, wherein the current detectors are arranged near the power elements, and the temperature detectors also serve as power element temperature detectors for preventing the overheating of the power elements.
According to a seventh aspect of the present invention, there is provided a motor controller, wherein the characteristics of the temperature detectors of the third aspect are prestored as data connected with the detection temperature of the ambient temperature detector, and the arithmetic and control unit comprises temperature computing means for computing temperature from the detection values of the temperature detectors based on data on the characteristics of the temperature detectors.
According to an eighth aspect of the present invention, there is provided a motor controller, wherein the arithmetic and control unit comprises means for creating current detection characteristic compensation data before the control operation of the motor, and the characteristics of the current detectors are measured to create the above current detection characteristic compensation data for compensating for fluctuations in the characteristics and to store them in the storage unit.
According to a ninth aspect of the present invention, there is provided a motor controller, wherein the characteristics of the current detectors are measured to create the current detection characteristic compensation data, accompanied by the switching operation of the power elements.
According to a tenth aspect of the present invention, there is provided a motor controller, wherein the arithmetic control unit comprises means for creating the current detection characteristic compensation data before the control operation of the motor, and the characteristics of the current detectors are measured by controlling the switching operation of the power elements based on detection temperatures from the current detectors to create the above current detection characteristic compensation data for compensating for fluctuations in the characteristics of the current detectors caused by temperature variations and to store them in the storage unit.
According to an eleventh aspect of the present invention, there is provided a motor controller, wherein the switching operation of the power elements at the time of creating the current detection characteristic compensation data is carried out so that a direct current runs through the current detectors.
According to a twelfth aspect of the present invention, there is provided a motor controller, wherein the current detection characteristic compensation data are stored separately for each of the current detectors and the computation of current values by the current value computing means is carried out for each of the current detectors.
According to a thirteenth aspect of the present invention, there is provided a motor controller, wherein the current detection characteristic compensation data are provided in the form of temperature compensation maps or temperature compensation expressions.
According to a fourteenth aspect of the present invention, there is provided a motor controller, wherein detection value data from the current detectors are collected together with temperature values detected by the temperature detectors of the fifth aspect such that the intervals between the temperature data values become a predetermined value with respect to an instruction current value running through the current detectors, and compensation maps are constructed with instruction current values, temperature data and detection value data collected by changing the instruction current value at predetermined intervals.
The above and other objects, features and advantages of the invention will become more apparent from the following description when taken in conjunction with the accompanying drawings.